Gas turbines embodied as aircraft engines have at least one compressor, at least one combustion chamber and at least one turbine. Aircraft engines are known from the state of the art, which on the one hand comprise three compressors positioned upstream from the combustion chamber, as well as three turbines positioned downstream from the combustion chamber. The three compressors are a low pressure compressor, a medium pressure compressor as well as a high pressure compressor. The three turbines are a high pressure turbine, a medium pressure turbine, as well as a low pressure turbine. According to the state of the art, the rotors of the high pressure compressor and the high pressure turbine, of the medium pressure compressor and the medium pressure turbine, as well as of the low pressure compressor and the low pressure turbine are connected with one another respectively by a shaft, whereby the three shafts concentrically surround or enclose one another and thus are nested within one another.
If, for example, the shaft connecting the medium pressure compressor as well as the medium pressure turbine with one another breaks i.e. fractures, then the medium pressure compressor can no longer extract or take up any work from the medium pressure turbine, whereby then an excessive rotational speed or over-speeding rotation condition of the medium pressure turbine can result. Such a free rotation of the medium pressure turbine must be avoided, because thereby the entire aircraft engine can be damaged. Thus, for safety reasons, a shaft break in a gas turbine must be surely detectable, in order to interrupt a fuel feed to the combustion chamber upon the occurrence of the shaft break. Such a detection of a shaft break presents difficulties especially when the gas turbine, as described above, comprises three concentrically enclosing shafts that are thus nested within one another. In this case, especially the detection of a shaft break of the middle shaft, which couples the medium pressure turbine with the medium pressure compressor, presents difficulties.